Image reading devices are used in paper-like media reading/screening devices and industrial inspection devices. For example, image reading devices are used in reading mark sheets, banknotes, and checks, and the like.
For reading banknotes or checks, special print may be made on their surface. For example, some banknotes are printed with invisible ink reflecting only the infrared light (wavelengths of 750 nm and longer) so as to enable the authentication of real banknotes. For the same purpose, some banknotes are printed with invisible ink emitting fluorescence when irradiated with the ultraviolet light (wavelengths of 300 to 400 nm).
For reading a banknote or check on which special print is made, it is required to irradiate the banknote or check with the infrared or ultraviolet light in addition to the visible light (wavelengths of 400 to 750 nm) used in reading ordinary print, and read the reflected light or emitted fluorescence from the banknote or check.
In order to solve the above problem, Patent Literature 1 discloses an image reading device comprising multiple light sources emitting light of different wavelengths from each other. The image reading device of the Patent Literature 1 comprises a first light source, a first light guide making the light from the first light source emerge toward a reading target, a second light source, a second light guide making the light from the second light source emerge toward the reading target and provided in parallel to the first light guide, and a lens unit and light receiving means provided between the first and second light guides, wherein the first and second light sources emit light of different wavelengths.
Furthermore, Patent Literature 2 discloses an ultraviolet irradiation device used in ultraviolet irradiation for fluorescence emission. This ultraviolet irradiation device comprises an LED emitting ultraviolet light and a light guide transparent to the light emitted by the LED, wherein the light guide is made of an amorphous fluorine resin and a linear light emerges via the light guide.
Schemes of making light enter a light guide made of a resin containing light-scattering microparticles from the rear face or a lateral end face thereof have problems with the assurance of focal illuminance and/or with uniformity. Then, in the ultraviolet irradiation device of the Patent Literature 2, multiple ultraviolet-emitting LEDs are lined up at fixed intervals and the light from the LEDs enters an elongated light guide transparent to the ultraviolet light. According to the Patent Literature 2, the lights emitted from adjacent LEDs overlap with each other at the ends of the fan-shaped lights, whereby a linear light source having a uniform light distribution is provided.